Double-acting press



AUS- 25, l942- w. ERNST i I DOUBLE-ACTING PRESS original Filed sept. 1e, 195s 3. Sheets-Sheet 1 27 EG. l

A TTORNE YS Aug. 2,5, l1942. w. ERNST Re. 22,163

' noUBLEAcTING PRESS original Filed sept. 1e, 1936 3 sheets-Sheet 2 /N VENTOR L TER EHA/6 7" ATTORNEYS Re.l 22, 1 63 Aug. 25, 1942. w. ERNST DOUBLE-Acum PRESS 3 Sheets-Sheet 3 Original Filed Sept. 16, 1936 INVENTOR WA LTER ,5R/V5 T A TTORNEYS UNITED STATES PATENT OFFICE noms-Ammo rnnss waiter Ernst, Manni einem, volii original No. 2,167,941, mea sums 1, 1939, se-

rial No. 101,110, september 1s, 193s. Application i'or reissue July 22, 1341, Serial No. 403,591

(c1.l 11s- 45) 13 Claims.

This invention relates to presses and, in particular, to hydraulic presses having blank-holding arrangements in association with drawing devices.

One object of this invention is to provide a hydraulic press having a clamping device arranged to provide. a plurality o1' different clamping pressures at different points on the blank, thereby enabling the blank to be held more tightly along diierent portions of its periphery.

Another Objectis to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers, together with means for maintaining different pressures in the different clamping plungers so as to hold the blank with diierent clamping pressures at different points, each clamping cylinder being arranged to enable the pressure therein to be adjusted independently of the pressures in the other clamping cylinders.

Another object is to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers, together with means for maintaining different pressures in the clamping plungers so as to maintain different clamping forces at diierent parts of the blank, additional means being provided to prevent the release of pressure from the clamping cylinder from tending to equalize the pressure in other clamping cylinders.

Another object is to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers 'operating in drawing and clamping cylinders, respectively, the pressure for operating the clamping cylinders vbeing provided by the action of the drawing plunger in forcing the clamping plungers downwardly against the blank, means being provided for releasing pressure iluid from the diierent clamping cylinders at different predetermined pressures so as to enable the blank to be held at different points by different clamping pressures.

Another object is to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers Operating in drawing and clamping cylinders, respectively, the pressure for operating the clamping cylinders being provided by the action of the drawing plunger in forcing the clamping plungers downwardly against the blank, meansfbeing provided for releasing pressure uid from the different clamping cylinders at diierent predetermined pressures so as t enable the blank to be held at different points by sure generated inthe clamping cylinders is utilized to torce the clamping member downwardly,

and thereby to assist the action of the drawing plunger instead of opposing it, as in other types .of presses.

Another object is to provide a hydraulic press having a drawing plunger and a plurality of clamping plungers arranged to provide different clamping pressures among themselves, together with release of pressure fluid therefrom on the attainment of diierent predetermined pressures therein, means being provided to prevent the escapeof pressure fluid upon the return stroke of the drawing plunger when the pressure releasing means is set at a low amount, thereby counteracting the effect of the pressurereleasing means during the return stroke oi' the press.

Still another object of the invention consists in the provision of a hydraulic blankholder press having a.V uid operable press platen and Ia clamping cylinder associatedtherewith, in which fluid pressure may be created in said clamping cylinder by movement of said blankholder and ymay be conveyed during movement of said platen to a stationarily mounted gauge so as to allow adjustment of a pressure relief valve, hydraulically connected with said clamping cylinder, while said platen is moving.

In the drawings:

Figure 1 is a diagrammatic View, mainly in section, showing the working elements of a hydraulic metal drawing press circuit arranged according to this invention, with the upper portion of the press framework omitted to show the construction more clearly.

Figure 2 is a horizontal section along the 'line 2- 2 in Figure 1.

Figure 3 is a view similar to Figure 1 but of a modified form of hydraulic drawing press eircit for accomplishing a similar result.

Figure 4 is a diagrammaticA plan view showing the connections between the various cylinders of the` press in Figure 3.

Figure 5 is a view yof a portion of Figure 3 of modified construction as regards the clamping cylinder.

Figure 6 is a vertical section through a pressure relief valve employed in connection with the press circuit shown in Figure 1.

In general, the press of this invention consists Aof a drawing plunger and a plurality of clamping plungers having relief valves associated with each clamping uplunger for release of the pressure iluid therein at predetermined pressures, thereby enabling the' different clamping plungers to exert different clamping pressures upon trie blank. There is also 'provided a ,series of check valves adapted 'to prevent the individual relief valves from interfering with the action Aoi' each other,y

`during the return stroke by admitting fluid to the opposite sideof the valve plunger, this arrangement enabling the moving part's to return on the return stroke, regardless ofAhow low the relief valve setting may be. l

The reason for providing audifferent clamping pressure at different portions of the blank arises from the fact that it is found thatl in drawing irregular work pieces it is often desirable to hold t one portion ofthe periphery of the blank with a tighter clamping force than other portions. In the ordinary types of presses, wherein the same clamping pressure is provided on all portions of the blank, this variable blankholding force canvnot be supplied. In the present invention,

however, each individual clamping cylinder is equipped with its ownr relief valve and its own check valve so that a different clamping pressure can be built up on each one of the several clamping plungers.

Referring to the drawings in detail, Figure 1 shows diagrammatically a hydraulic metal drawing press having a base member Iii connected to a top member II (reduced in size for clearness of showing) by means of tie rods I2, the latter being secured in position by means of the nuts I3 upon the ends thereof. Mounted in the base member II) is a drawingdie I4having a die cavity- I5 for receiving the blank I6. Associated with the die cavity I5 is a plunger I1 adapted to support the -tip ofthe blank as itis being drawn, and passing through a bore I8 to its operating cylinder (not shown). The details of the supporting plunger I1 form no part of the present invention, and are shown in my copending application, Ser. No. 74,742, filed April 16, 1936, and now matured into Patent No. 2,136,240 granted Nov. 8, 1938.

The present invention may be employed either with fiat blanks or with blanks whichhave a1 ready been subjected to one or more drawing operations.' For convenience of disclosure, blank I6 is shown as having been subjected to one` drawing operation, and in position for another drawing operation which will elongate it and cause it to be drawn downwardly into the die cavity I5.

Associated with the top member I I of the press is a surge tank I9 for containing the fluid by which the press is actuated. Also associated with the top member II is the drawing or main cylinder 2|)having a bore 2i Within which reciprocats the double-acting drawing plunger 22 having a piston head 23 thereon. The cylinder 20 is provided with upper and lower ports 24 and 25 on kopposite sides of the piston head 23, and adapted by means of pipes 26 and 21 to supply pressureifluid to advance or retract the drawing plunger 22, according to the manner in which the four-wayvalve 28 is manipulated. This valve 28 is` of any suitable `typeknown to those skilled in the artyand its details form no npart of the present invention. l

Leading from the four-way valve 28 is the pressure line 29 connected at its opposite end to' the pump 30. A discharge line 3i, also connected to the four-way valve 28', leads into the interior of the surge tank I9. The pump `3Il is also provided with a suction line 32, likewise leading into the interior of the surge tank YI9. The drawing cylinder 20 is supplied near the mouth of its bore 2l with a packing ring 33, beyond which is a packing 34 adapted to be compressed by a gland 35 so as to prevent leakage around the drawing plunger 22. Connected to the drawing plunger 22 is the platen 36, within which are arranged the clamping cylinders 31 having clamping plungers 38 operating therein. Each clamping plunger 38 is provided with a packing 39 and gland 4U for the prevention of leakage. Secured to the platen 35 is a drawing plunger or punch 4I having a nose portion 42 corresponding to the diejcavity I5, and adapted to pass through an aperture 43 in the clamping member 44 secured to the outer ends of the clamping plungers 38.

Each of the clamping cylinders 31 is provided with a uid passageway 45 leading by way of an outwardly opening check valve 46 to a common passageway 41, which extends upwardly through the drawing plunger 42 and opens into the drawing cylinder bore 2I immediately beneath the drawing plunger head 23. Consequently, fluid is free to pass from the pull-back or return side of the drawing plunger 23 into the clamping' cylinders 31, but is prevented from passing in the oppos-ite direction by the action of the check valves 46. Also passing outwardly from each clamping cylinder 31 is a fluid conduit 48 leading to an intermediate portion of a pipe 4S, having on one end a safety valve 50 and on the other end a pressure relief valve 5I. Leading from the discharge side of the safety valve 50 is a discharge line 52 connected to the discharge side of the relief valve 5I by the line 53.'4

'I'he discharge line 52 passes upwardly into the telescoping cylinder 54, thereby forming a slip connection, enabling the telescoping cylinder 54 and the, pipe 52 to move vertically relatively to each other, an action which neces- `sarily occurs when the platen 35 moves downwardly in response to the action ofthe drawing plunger 22. A discharge line 55 leads from thepressure than the relief valve 5I so as to oper-` ate in case of the accumulation of a dangerous pressure, within the corresponding clamping cylinder 31 and a failure of the corresponding pressure relief valve 5i to act. It will be seen from` Figures 1 and v2 that each clamping cylinder is provided with its own pressure relief valve 5I and safety valve 5D so that a different pressure release point may be given to `each clamping cylinder. Thepressure relief valves 5I are connected to the drawing plunger passageway 41 by conduits 56 for the purpose of counteracting the action of the relief .valves 5I `during the re- .turnstroke ofthe drawing plunger 22, as is disthe pipe into engagement with motion -between the platen The relief valve I is shown in -vertical section in Figure 6, and consist of a casinghaving a bore 6I within which reciprocates a valve plunger 62. Arranged between the valve plunger 62 and the bore 6I is a tubular member 63 having a longitudinal bore 65 and a cross bore 66, communicating therewith and opening .into a transverse bore 61 in the casing 60. The end connection of the pipe 49 is held in communication with the bore 6I by means of the collar 63 engaging the threaded portion 69 of the casing 66, whereas .the end of the pipe 53 is. similarly held in communication with the transverse bore 61 by means of the threaded collar 10 engaging the threaded portion 1I of the casing (Figure 6).

Mounted on the upper portion of the casing 69 is a tubular cap 12 secured thereto by screws 13, within the cap 12 is a coil spring 14, one end of which engages an enlargement 15 upon the upper end of the valve plunger 62, whereas the opposite end engages a button 16 in contact with an adjusting screw 11 threaded through a bore 19 in the upper end of the cap 12. Surrounding and covering the adjusting screw 11 is a hollow nut 19 which serves to protect the adjusting screw 11 and also to lock it in its adjusted position. The cap 12 is 'provided with a port 56 leading to the pull-back side of the plunger 22, as shown in Figure l. Thus, when the same pressure fluid is admitted simultaneously to the valve 5I, lby way of the pipes 49 and 56 during the pull-back stroke of the press, the valve plunger 62 will be prevented from opening by means of this counteracting arrangement, as is more fully described under the operation thereof. The pipe 56 also serves durdrawing 60 receiving and communicating with,

ing the return stroke of the press to receive and which leaks into the interior of the cap 12 past the valve plunger 62. Thus, each safety valve 5| may be adjusted to discharge pressure fluid at a different predetermined pressure by differently adjusting the adjusting .screw 11 to compress the springs 14 by different amounts. The clamping member 44 is provided with rods 8I passing through the vertical bores 82 in the platen 36, and having the nuts 63 on the upper ends thereof. The rods 6I limit the extent to which the clamping member 44 can move relatively to the platen 36.

In the operation of the form of press shown in Figures 1 and 2, the pump 30 is started and delivers pressure uid to the four-way valve 26, which in turn, is set to deliver pressure fluid through the line 26 and port 24 into the space above the drawing plunger head 23. 'Il'iis pressure forces the drawing plunger 22 and platen 36 downwardly, carrying with them the clamping member 44. When the latter engages the periphery of the blank' I6 and clamps it tightly against the die member I4, the clamping member 44 halts, but; the platen 36 continues to move downwardly, forcing its drawing die or punch 4I the blank I6. As the punch 4I moves downwardly it forces the central portion of the blank I6 into the die cavity I5 and overcomesy the resistance of the supporting plunger I1, which protects the tip of the work -piece or blank I6.

Meanwhile, pressure has ibeen built up in the clamping cylinders 31 by reason of the relative 36 and the clamping clamping plungers 36 transmit the fluid member 44 to which the are attached, and the fluid in the clamping cylinders 31 has been prevented from escaping by the closing of the outwardly opening check valves 46. When the pressure within each clamping cylinder 31 reaches the amount for which its corresponding relief valve 5I is set, the latter opens and discharges fluid through the line 53, into the discharge line 52 leading to the telescoping cylinder 54, and thence by the line 55 to the surge tank I9. In this manner each clamping plunger 38 may be caused to exert a different force upon the portion of the blank periphery which is engaged by the clamping member 44 in its vicinity. y ,Y

When the drawing strokev of the press has been completed the setting of the four-way valve 26 is reversed so that pressure uid flows through the line 21 and port 25, into the space beneath the drawing plunger head 2,3, causing the drawing plunger 22 to move upwardly. A portion wardly opening relief valves 46, to the passageways 45, into the clamping cylinders 31, causing their plungers 36 and the clamping member 44 to remain in clamping engagement with the blank I6 while the punch or drawing die 4I is withdrawn from the cavity I5 of the die I4. If the relief valves 5I have been 'set for alow clamping pressure it would, at first glance, seem that pressure fluid during the pull-back stroke would pass from the clamping cylinders 48 through the relief valve 5I and lines 52, 53 and 55, back into the surge tank I9, thus preventing the return of the moving parts. This, however, is prevented by the operation lof the pipe line 56 leading from ,the valve cap 12 ofthe valve 5I to the passageway 41 within the drawing plunger 22. Consequently, during the pull-back stroke pressure fluid is applied simultaneously upon opposite sides of the valve plunger 62 within the relief valve 5I, and prevents its opening regardless of how low a clamping pressure is provided by the setting of each relief valve 5I. When the platen 36 has moved upwardly along the rods Illy it will engage the nuts 83 and lift the clamping member 42 free from engagement with the work piece I6, thereby enabling the operator to remove the work piece and also lifting the entire platen and blankholder assembly as a unit.

The modified form of press shown in Figures 3 and 4 has a base portion Ill, tie rods I2, die I4 and supporting plunger I 8 similar to those o! the press shown in Figure 1. A pump 30 and four-way valve 48 are similarly provided, and

the latter has similar forward and reverse pressure lines 26 and 21I respectively, leading to the opposite sides of the drawing plunger head 23 within the drawing cylinder 20. Other corresponding parts are given likereference numerals. In this form of press, however, the drawing plunger 22 is of solid construction, and the clamping plunger cylinders 31 are provided with passages 61 leadinginto tubular plungers 68 mount- -ed upon the upper side of the platen 36, and hav- I hollow plungers leads through the checktive stationary gauge, so

'by member 44 is subtracted from the useful drawsired proportion of the pressure on -valve 28 isset to discharge pressure From each cylinder 92 a f-shaped line 95 also leads to a safety valve 96 and a pressure relief valvev 91. These valves 96 and 91 are slmilar to the safety valves valves 5I described in connection with Figure 1, with the exception of the fact that the connection 56 to the port 80 in the`valve cap 12 is omitted. The valves 96 and 91 discharge into the discharge line 98 leading to the interior of the surge tank I9. A pressure gauge 99 is provided in each line`95 to indicate the pressure existing in the clamping cylinder 31. Inasmuch as the cylinder 92 is stationary, it will be clear that also the conduit 95 and gauge 99 can be arranged stationarily. This is of great importance since, in this way, the clamping pressuredeveloped in each clamping cylinder can beread on a respecthat the adjustment of the relief Valve 91 may be effected while the platen 36 is moving. Extending from each cylinder 92 is a line |00 having therein a check valve |0I opening in a direction away from the cylinder 92. Beyond the check valves I|l|'v the lines |00 join a common line |02 leading to a normally open valve |03, having a discharge line |04 leading therefrom to the surge tank |9. The

valve|03 is provided with a valve rod |05 having an adjustable stop engaged by the end cured to the platen 36. The platen 36 is provided with bores |09 adapted to receive the rods II0,

|06 thereon adapted to be 50 and pressure relief platen 36 has descended 4stop |06 and moved |01 of a platen armv |06 se-` the lower ends of which are secured to the clampl ing member M, and the upper ends of which are provided with nuts III threaded thereon. The upper ends of the rods |I0 are also provided with threaded sockets |I2 in which are inserted the threaded rods |I3. This arrangement enables an adjustment of the effective length of the rods IIO and enables thepoint at which these rods I|0 serve as knock-out rods to be varied as desired.

In ordinary drawingpresses it will be seen that during a drawing operation the pressure exerted the clamping plungers 38 and the clamping ing force exerted by the drawing plunger 22 because the drawing plunger 22 must overcome the intensified pressure on the clamping plungers 38 withinv the clamping cylinders 31. Where the clamping pressures are low, the efect of this arrangement is not serious. If, however, a high pressure is employed for clamping the blanks the reduction in drawing force by the withdrawal of force for the clamping plungers may be quite serious. It is for this reason that the modified arrangement shown in Figure 3 was devised. The pressure generated by the relative 4motion between the platen 36 and the halted blankstill produces the holder or clamping member 44 blankholder clamping pressure, but this pressure now iiows through the hollow plungers 88 and helps to advance the platen 36 by operating on the annular heads of the plungers the clamping plungers 38 can thus be balanced, and the main or drawing plunger 22 will only have to overcome the difference between the pressures on the ends of the plungers 38 and 88. In this manner it is possible to exert very great clamping pressures 88. Any de-' 22 then moves downwardly, carrying with it the Y platen 36 and the hollow plungers -88.

The suction thereby created in the cylinders 92 opens the checkvalves 94 and causes fluid to be drawn into the cylinders from the surge tank I9. When the blankholder or clamping member 44 descends to a pointv where it engagesthe work piece I6, however,`a relative motion occurs between the now halted blankholder 44 and platen 36 as the latter continues to advance and move its drawing die or punch 4I into'engagement with the work piece I6. Pressure thus accumulates in the clamping cylinders 31 and is transmitted through the passages 89 of the hollow plungers 88 into the. cylinders 92. Normally this pressure would be free to pass through the lines |00, check valves |0I, line |02, normally open valve |03 and line |04 into the surge tank I9. By this time, however, the to a point whereat the end |01 of the platen arm |00'has engaged the the valve rod |05 downwardly, thereby closing the normally open valve |03 and cutting off this means of escape for the iiuid from the cylinders 92. The check valves 94 in the lines 93 also close against the'pressure in the cylinders 92. This Ileaves the lines 95 as the sole means 'of escape forthe uid. Consequently, when the pressure in each line 95 exceeds the setting of its relief valve 91, the latter will open and discharge uidthrough its discharge line98 into the surge tank I9. In the event that the pressure relief valve 91 jams or fails for other reasons, the safety valve 96, which is set for a higher pressure, will open and discharge the fluid, thereby preventing damage to piece I6. The

the press. By adjusting the relief valves 91 to discharge at different pressures the clamping cylinders 3I`,and their clamping plungers 38 may be caused to exert different clamping pressuresupon the clamping .member of blankholder Il, and hence, apply different amounts of pressure'to different pointscn the periphery of the work check valves |0| prevent the equalization of pressures between the several cylinders 92, consequently, the intensified pressure built up in the clamping cylinders 31 acts against the clamping plungers 38 to clamp the work pieceV I6. At the sainev timea portion of this pressure fluid passing through the bore 89 of each hollow plunger 88`acts against' the annular top surface thereof, and urges each plunger 88 in a downward direction, -thereby assisting the action of the main ordrawing plunger 22.

. in a closed position,

with comparatively small ,main 0r drawing plunger pressures. y

In the operation of the press and circuit shown inFigures 3 and 4, the pump30 is started and fluid through the forward line 26 leading to the space above the in the cylinders 92 As soonas the drawing operation has been completed, the operator shifts the four-way control valve 28 to cause the pump 30 to discharge pressure fluid through the line 21 into the" space beneath the drawing plunger head 23. This pressure raises the drawing plunger -22 and the platen 36, together with the hollow plungers 88.` At the start of this operation, however, the platen arm |08 is still holding the normally open valve |03 hence, the plungers 88 canthe pressure already built up without displacing fluid into the clamping cylinders 31 within the platen 36. This pressure fluid, so displaced, acts against the clamping plungers 38 and tends to separate the platen 36 and the clamping member or blankholder 44 until both have traveled a distance suflicient to enable the platen arm |08 to release not return against thei valve |03 tion. When this occurs the cylinders 92 through the lines |00, the check vvalves IUI, the line |02, the valve `|03 and the line I 04 into the surge tank |9,' permitting the entire assembly to execute its return stroke. The adjustable arrangement shown on the rods serves to separate the platen 36 and the blankholder M in a positive manner in case both of these shouldbe held together by reason of the work piece I6 adhering to the drawing die or punch 4|.

Thus by the present invention a full' blankholding pressure can be exerted by supplying only a fraction of it by means of the main or drawing plunger 22, through the aid of the `hol low plungers B8. The arrangement of the check valves |0| and the normally open platen-closed valve |03 enables the pressure to be released through the single valve ID3 without, however, equalizing the pressures in the cylinders 92. Without the check-valves |0| the pressures in all cylinders would equalize, thereby defeating the purpose of the individual relief valvesA 91.

In the arrangement shown in both forms of presses in Figures 1 and 3, respectively, the main or drawing cylinder 2U has been shown arranged for descent merely by pressure from the pump 30 through the line 26. It will be understood, however, that a surge valve may be mounted in the top of the cylinder 20 and operated in the manner lshow n in my copending application, Ser, No. 74,742, led April 16, 1936, thereby enabling the descent of the drawing plunger 22 by gravity and the prefilling of the cylinder 20 through such a surge valve. This surge valve has been omitted from th'e present circuits for the purpose of simplifying the showing.

'I'h'e modified construction shown in Figure 5 has the same purpose as the hollow plungers 88 and cylinders 92 in Figure 3. In this arrangement, however, the blankholder or clamping member" 44 is provided with clamping cylinders IIS in upwardly projecting portions Ill -adapted to entercorresponding recesses ||8 in the platen 36.

Glands I |9 and packings |20 prevent the escape of fluid from around the hollow clamping plungers |2I, these being mounted in bores |22 inv the upper walls of the recesses I|8 in the platen 36. Each plunger |2| is provided with an enlargement |23 adapted to engage the upper or end wall of the recess H8. Formed integral with the clamping plungers |,2|, in this arrangement, and extending vertically upward therefrom are the hollow .plunger portions |24 leading into the icylinders 92, previously described. While this construction is a modifica- Having thus fully described my invention, what I claim as-new and desire to secure by Letters Patent, is:

1. In combination in a drawing press, a press frame having a main cylinder and an auxiliary cylinder, a main plunger in said main cylinder,

a platen operated thereby, a hollow auxiliary.

plunger connected to said platen and reciprocable in said auxiliary cylinder,a clamping cyl.

inder associated with said platen and communicating with said hollow auxiliary plunger, a clamping plunger adapted to clamp the work piece during the drawing operation, and an adjustable pressure relief valve for said clamping cylinder adapted to effect the discharge of pressure fluid 1from said clamping cylinder at a predetermined pressure, the working surfaces on the heads of said auxiliary plunger and main plunger being positioned in similar directions relatively to said platen whereby the pressure fluid generated in said clamping cylinder duri/ng the clamping operation acts against said auxiliary plunger to assist the urge imparted to said platen by said main plunger. y

2. In combination in a drawing press, a press head having a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders mounted on said press head, auxiliary hollow plungers connected to said platen and communicating with said clamping cylinders and reciprocable in said auxiliary' cylinders, and a pressure relief device for each auxiliary cylinder adapted to discharge -iiuid therefrom in response to the attainment of operated by said drawing plunger, clamping pistion of that shown in Figure 3, the operation is substantially identical and requires no additional description.

It will be understood that a separate pressure may be applied to each clamping plunger by employing a different pump foreach clamping plunger rather than a single pump with four dif.` ferent pressure relief valves. In this vmanner each pump may be set to deliver the predetermined and desired pressure to its own particular clamping plunger. In Figure 3, instead of the hollow plungers shown, solid plungers may be used with any suitable arrangement for co'nton and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary hollow plungers connected to said clamping cylinders and reciprocable in said auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attainment of a predetermined pressure therein, a con'l duit adapted to discharge fluid from said auxilducting fluid from the clamping cylinders 3| to f l' the cylinders 92, such as, for example, a flexible conduit.

`It will be understood that I desire to comprehend within this invention such modifications v 'as comwithin the scope of the claims and the inventiol E" iary cylinders, a normally open valve in said conduit, and means responsive tothe attainment of a predetermined position of said platen for closing said normally open valve to prevent the further discharge of the fluid through said conduit.

4. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston `and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary hollow plungers connected to said clamping cylinders and reciprocable in said auxiliary cylinders. a pressure relief device for each auxiliary cylinder adapted to discharge fluid' therefrom in response to the attainment of a predetermined pressure therein, a conduit adapted to discharge fluid from said auxiliary cylinders, a normally open valve in said conduit, means responsive to the attainment of predetermined position of said platen for closing said normally open valve to prevent the further discharge of the fluid through said conduit, and unidirectional means in said conduit for permitting the now of fluid from said auxiliary cylinders to said normally open valve but adapted to prevent the ilow of iluid from one auxiliary cylinder to another auxiliary cylinder.

5. In combination in a drawing press, a drawing cylinder, a drawing plunger therein,`a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said 'i platen and operated by the motion thereof, auxiliary cylinders, auxiliary hollow plungers connected to said clamping cylinders and reciprocable in said ,auxiliary cylinders, a pressure relief device for each auxiliary cylinder adapted to discharge fluid therefrom in response to the attain- 1 ment of a predetermined pressure therein, a fluid tank, a conduit connecting each auxiliary cylinder with said fluid tank, and a check valve in said conduit for permitting the drawing in .of fluid in response to the suction created in said auxiliary cylinders by the descent of said auxiliary plungers. l

6. In combination in a drawing press, a press head having a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblis associated with said platen and operated by themotion thereof', auxiliary cylinders mounted on said press head, auxiliary plungers movable in said auxiliary cylinders and connected to said p1aten,mea.ns for conducting iluid between said clamping cylinders and said auxiliary cylinders,

and a pressure relief device foreach auxiliary cylinder adaptedto discharge fluid therefrom in,y

response to the attainment of a predetermined' pressure therein. `the working surfaces on the heads of said auxiliary plunger and said drawing plunger. being positioned in similar directions relatively to said platen, whereby the pressure fluid generated in said clamping cylinders during the clamping operation acts against said auxiliary plungers to assist the urge imparted to said platen by said main plunger.

7. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen n operated by said'drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary plungers movablejin said auxiliary cylinders, means for conducting fluid between saidv clamping cylinders and said auxiliaryV cylinders, a pressure relief device for each lauxiliary cylinder adapted to discharge Vfluid therefrom in` response to the attainment of a. predetermined pressure therein, a conduit adapted Ito discharge fluid from. said auxiliary cylinders, a normally open valve in said conduit, andmeans responsive ,to the attainment of a predetermined position of said platen for closing said normally open valve to prevent the further discharge of fluid through said conduit.

`il. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary plungers movable in said auxiliary cylinders, meansfor conducting l fluid between said clamping cylinders and said auxiliary cylinders, a pressure relief device for each auxiliary cylinder 4adapted to discharge fluid therefrom in response to the attainment of a predetermined pressure therein, la conduit adapted to discharge fluid from said' auxiliary cylinders, a normally open valve in said conduit, means-responsivefto the attainment of a predetermined position of said' platen for closing said normally open valve to p revent the. further discharge of fluid through said conduit, and unidirectional means in said conduit for permitting the now of fluid from said auxiliary cylinders to said normally open valve but adapted to prevent the flow of fluid from one auxiliary cylinder to another auxiliary cylinder.

9. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by-said drawing plunger, clamping piston and cylinder assemblies associated with said platen and operated by the motion thereof, auxiliary cylinders, auxiliary plungers movable in l said auxiliary cylinders, means for conducting fluid between said clamping cylinders and said auxiliary cylinders, a pressure relief ydevice for each auxiliary cylinder'adapted to discharge fluid therefrom in response to tl'ie` attainment of a. predetermined pressure therein, a fluid tank, a conduit connecting each auxiliary cylinder with said fluid tank, and a' check valve in said conduit forl permitting thevdrawing in of uid in response to the suction created in said auxiliary cylinders by the descent of said auxiliary plungers.

10. In combination in a drawing press, a drawing plunger, a platen operatively connected with saidy drawing plunger, fluid operable clamping cylinder-piston-assemblies associated with said platen and operable by the motion thereof, a plurality of stationarily mounted pressure relief devices, at least two ofsaid relief devices being associated with two separate cylinders of said clamping cylinder-piston-assemblies and being adapted to discharge fluid therefrom in response to the establishment of a predetermined pressure therein, a plurality of stationary conduits, each being connected with one yof said relief devices, means respectively associated with each of said clamping cylinders and continuously hydraulically connecting each clamping cylinder with one of said conduits, and pressure gauges respectively connectedwith said stationary conduits for indicating the pressure in the respective clamping cylinder during movement of said platen.

ll. In a hydraulic blankholder press, a fluid operable press platen, fluid operable clamping cylinder-piston-assemblies associated with said platen and adapted to Ydevelop pressure in response tothe movement of said platen,` stationarily mounted adjustable reliefl valves respectively associated with the cylinders of said clamping cylinder-piston-assemblies for relieving pressure .therefrom at the establishment of a predeter- `continuously establishing hydraulic connection between said cylinders and the respective relief valves.

12. In a blankholder press, a fluid operable drawing platen, a fluid operable cylinder-piston- Y assembly associated with said platen andY adapted to develop pressure by movement of said platen, a stationarily mounted pressure relief valve associated with said clamping Cylinder-piston-assembly for relieving pressure therefrom in ing cylinder-piston-assembly, and a gauge arranged at a stationary point of the press and in y excess o! a predetermined pressure in said clam continuous hydraulic communication `with said valve, said gauge communicating through connecting means with said clamping cylinder-piston-assembly :or indicating the clamping pres` sure in said cylinder-piston-assembly during movement of said platen,

13. In combination in a drawing press, a drawing cylinder, a drawing plunger therein, a platen operated by said drawing plunger, a clamping' cylinder-piston-assembly associated with said platen and operated by the motion thereof, said clamping cylinder-piston-assembly including an auxiliary cylinder and a hollow auxiliary plunger' reciprocable in said auxiliary cylinder, a pressure relief device associated with s aid clamping cylinder-piston-assembiy to discharge fluid therefrom in response to the attainment of a prede- 4 terminedpressure therein, a iluid tank, a conduit connecting said clamping cylinder-pistonassembly with said uld tank, and a check valve ior permitting the drawing in of fluid in response to the suction created in said clamping cylinderpiston-assembly by the descent oi the platen.

WALTER ERNST. 

